m73m95

I really like the "bird chirp" sound some turbo cars have when they come off throttle. I have a couple of questions about it.

First, how is the sound made? Is it from the wastegate, or the BOV? is it possible to get this sound on a 951?

Second, how does it affect performance (or does it)?

(I was going to get a video of the new Mclaren MP4-12C to illustrate the sound I'm talking about, but I can't find a video of someone driving it. Jeremy Clarkson drove one on Top Gear, but I can't find the video. Maybe someone can post it)

Hopefully you call know the sound I'm talking about.

Thanks,

CPR

BOV...and yep it is there

minho78

Yup it's the BOV. I thinks HKS makes that type.

Techno Duck

It depends on the type of bypass/ blow off valve you use. The ones with the loud whistle are more than likely blow offs dumping to atmosphere. This is not ideal for the 951 as you are dumping metered air and this will cause a rich condition on throttle lift making for a nice fireball out the tailpipe usually and the other not so nice effects of running rich. One very annoying aspect ifthis is stalling when comi off throttle which can happen on occasion. You can tune for that richness though.

They make valves which are semi recirculating to get around this. They also make screw on stacks for the dump side that allow you to 'tune' the sound it makes when it dumps.

I think the best sounding bypass valve is the old, purple top Greddy Type-S. It's a diaphragm type and makes a very distinct sound when you lift. My friend has one on his WRX and it sounds great, always turns heads. The downside is they are not very durable. Also they are no longer made and command a premium now days.. The replacement Type-RS I here sucks.

I personally like the 'flutter dump' I get, only get it when lifting from full boost though.

m73m95

^^ Thats what I wanted to know!!

Thanks for the details Jon.

I have read posts about recirculating the pressure, and not venting to atmosphere, but I didn't know what the advantages/disadvantages are.

Having a fireball out the back isn't a bad thing either! (visually speaking anyway)

Why do some factory cars (evo's, Zonda's etc.) do this? Is the sound and fire just for visual effect at the expense of the engine, or is there really no detrimental harm to the engine because the richness is just momentary?

aixgelo78

forget the bird call..... try this:

http://www.youtube.com/watch?v=VbNxugO-uf0&feature=fvw

or

http://www.youtube.com/watch?v=Erjhk...eature=related

m73m95

oh dude..... ^^

DanR

PMSL

beebone

You can serach "BOV duck call" in Youtube, is it the right chirp u looking for?!?!?! Its funny

minho78

Man you made roll on the floor with that BOV.

odb812

you can definitely hear my valve and i have it hooked up to recirculate. i have a forge billet dv and aluminum ic pipes.

drift a 944

I'm also curious to know. Are there any other ill effects to running an atmospheric BOV other than a fireball and possibly cutting off upon returning to idle?

I am using a brand new EVO Motorsports DV with the stock AFM and a drop-in cone filter, and can't hear any noise. Soon I will be installing my Lindsey Racing Stage-2 MAF and K&N which I am hoping will make the DV more audible... but will it?

PixxByTango

The BOV will dump to atmosphere whereas the Bypass valve is designed for a closed loop operation. Having a Bypass is primarily designed to keep the turbo from compressor surge or worse failure. Remember that the turbo runs not on a bearing but simply the shaft is suspended on a film of oil within a bushing. This small tolerance is disrupted when the turbo has a surge from a closed throttle. Forget about worrying of flame or rich mixtures... think about much more expensive parts. A properly setup system will have the bypass valve as close to the throttle body butterflies as can be. This way the charge air pipe has a supply of airflow ready upon the acuation of the throttle between shifts to minimize lag of the turbo having to re-charge the up-pipe to the throttle body. Can you visualize this?

Imagine how much air volume is flowing in the pipe to create two atmospheres of boost in your engine... now think of where that air has to go if you immediately close the throttle from a redline wot shift. Without a BOV or bypass the compressor will surge and cause a horrible flutter sound that some actually like to hear not knowing its damaging parts. Having a properly sprung and metered BOV or Bypass will alleviate this problem and if done right can increase throttle sensitivity/performance.

I even have a BOV on my Yamaha Waverunner because running anything higher than the factory 6psi of boost will destroy the sprag clutch mechanism that spins the supercharger. Since my system is unmetered, my BOV just dumps to the atmosphere. I use a HKS copy BOV that cost $50 from http://www.frozenboost.com I've had GREAT luck with their parts and AMAZING customer service!

gt37vgt

perhaps you are after the sound of running no blow off ..
cars running around 1 bar or more sound awsome with no blow off they give a "choo choo cha " sound ..
bad news is its compressor surge and destroys turbos ..
but newer ball bearing turbos are more durable and can take it a lot longer

gt37vgt

ok here it is compressor surge sounds great but not good for performance or turbos
http://www.youtube.com/watch?v=CJlR_zIwmiE